Geoff,
""One thing that concerns me is the ride height of the body at the rear. Some replicas appear to have considerable clearance between the top of the rear tyres and the bodywork.""
Couple of reasons for this that I've seen. When the original cars are set up to race they have less ground clearance than when their on the road. This lowers the whole car body and all, with the same size tire it's closer to the body. But a road car with clearance for speed bumps etc sits higher so with the same size tire you going to have a gap.
Shock travel and spring rate could be a factor also typically a race shock has less travel and stiffer springs than a road one hence not as much clearance is needed with the race unit. Tire size could be a factor also. Some of the kit manufactures may be giving a little more clearance compared to
a race setting were performance is enhanced by getting the clearance as close as possible.
I have a friend that races a GT40 MarkV, (quiz, which one is this?) at the historic races his shocks have about 3/4" bump travel and 450lbs springs on the front as opposed to a road car with 1-1/2" 300lbs. This car also has about 1-1/2" less ground clearance than a road unit. And I do note that the edge of the fender lip is actually below the top of the tire as compared to the car I'm building which has about 1" clearance.
""Ray Mallock Racing always emphasised that the reason they used a ZF 'box was that the engine sat lower in the car, as on the original.""
Here's the way I figured this. The original pan depth is 6", and the bottom of the pan is flush with the bottom of the car. That puts the crankshaft center line at 6" from the bottom of the car. (The 302 crank center line is flush with the pan gasket surface) So now your criteria for choosing your transaxle is
that it can be no more than 6" from the input shaft centerline to the bottom of the bellhousing or trans case. Otherwise you have to raise the engine to maintain ground clearance of the Taxle.
I lucked totally on this because I bought the G50 Taxle knowing only that others had used it sucessfully. I didn't really measure the G50 but it just so happens that when it's inverted as is necessary the bell housing is the lowest point and the diameter of the bell housing is 12", so 6" radius. This is the lowest you're going to get it as this is probably the smallest bellhousing your going to see due to flywheel/clutch size constraints.
The only problem I see with the G50 is that the axle flanges sit a little high so there's going to be some droop angle to the CV shafts at ride height (robs power). Not sure how much yet but I do note that a real GT40 with a ZF box has 3 deg droop and that's with 3.5" ground clearance.
This raises another factor. Due to transaxle design the centerline of the axle flanges is either above or below the input shaft centerline (they have to cross each other in the box) so this decides whether your axles droop a little or your engine is higher than you'd like.
Sorry this got a little long but it does show that things are not always as simple as they seem, and also demonstrates how much time and effort went into the design of the original and the current replicas.
[ January 02, 2002: Message edited by: Kalun D ]
